Cyanophycin is a natural biopolymer produced by a wide range of bacteria, consisting of a chain of poly-l-Asp residues with l-Arg residues attached to the β-carboxylate sidechains by isopeptide bonds. Cyanophycin is synthesized from ATP, aspartic acid and arginine by a homooligomeric enzyme called cyanophycin synthetase (CphA1). CphA1 has domains that are homologous to glutathione synthetases and muramyl ligases, but no other structural information has been available. Here, we present cryo-electron microscopy and X-ray crystallography structures of cyanophycin synthetases from three different bacteria, including cocomplex structures of CphA1 with ATP and cyanophycin polymer analogs at 2.6 Å resolution. These structures reveal two distinct tetrameric architectures, show the configuration of active sites and polymer-binding regions, indicate dynamic conformational changes and afford insight into catalytic mechanism. Accompanying biochemical interrogation of substrate binding sites, catalytic centers and oligomerization interfaces combine with the structures to provide a holistic understanding of cyanophycin biosynthesis.

蓝藻素是一种由多种细菌产生的天然生物聚合物，由带有l -L - Asp 残基的链组成。-Arg 残基通过异肽键与 β-羧酸酯侧链相连。蓝藻素由 ATP、天冬氨酸和精氨酸通过称为蓝藻素合成酶 (CphA1) 的同寡聚酶合成。CphA1 具有与谷胱甘肽合成酶和胞壁酰连接酶同源的结构域，但没有其他结构信息可用。在这里，我们展示了来自三种不同细菌的蓝藻素合成酶的低温电子显微镜和 X 射线晶体学结构，包括 CphA1 与 ATP 和蓝藻素聚合物类似物的复合结构，分辨率为 2.6 Å。这些结构揭示了两种不同的四聚体结构，显示了活性位点和聚合物结合区域的配置，指示了动态构象变化并提供了对催化机制的深入了解。